1. Field of the Invention
This invention relates to electronic means for observing and/or measuring certain properties of the blood circulation in a living body.
2. Discussion of the Prior Art
Maintenance of life and viability of tissue cells depends on the physiological movement of blood in capillary circulation. The capillary circulation is contained by the small blood vessel network within which it is embraced between arterioles and venules. The capillary system is the interface between arterial and venous blood through all body tissue. The small vessel circulation is commonly referred to as the micro-circulation.
The blood volume is contained by the micro-circulation and the macro-circulation.
The macro-circulation includes the heart and blood vessels external to the micro-circulation. Traditional parameters of E.C.G., B.P. etc. are directed at the macrocirculation. Macrocirculatory parameters do not measure or reflect capillary activity or the effect of microcirculatory fluctuations.
The Stephens Tissue Perfusion Monitor or STPM (the subject of my Australian Pat. No. 465,302) samples and quantifies a signal from capillary circulation near skin surface to produce a measurement which is derived colorimetrically and non-invasively from micro-circulation in skin. The measurement, the Tissue Perfusion Index (TPI), is able to follow microcirculatory fluctuations and so provides indication of stability or change in activity of pulsatile micro-circulation at capillary level relative to an absolute reference level (say, 500 mV).
However, blood flow is a rhythmic activity capable of precise mathematical representation of curve shape in a sequence of analogue pulse curves. Despite the value of such a parameter as the TPI, the existing Tissue Perfusion Monitor is not intended to distinguish between differently shaped curves having the same area beneath them.